Hoping to take the lead in the race to build the ultimate wearable device, Samsung offered a sneak peak Wednesday at its next-generation health-tracking wristband, known as the Simband. Using different wavelengths of light beamed at your skin, Simband will track multiple measures of its wearer’s health continuously, such as blood pressure, respiration, heart rate, hydration level, and the amount of carbon dioxide in your blood. The one Simband demonstrated on stage at Samsung’s “Voice of the Body” event in San Francisco showed a continuous stream of heartbeat information, seismograph-style, such as one might see on a hospital-grade ECG machine. A “shuttle battery” will allow you to wear the device 24 hours a day, charging it on your wrist while you sleep.